GB1383960A - Semiconductor laser - Google Patents

Abstract

1383960 Use of luminescence and electroluminescence LICENTIA PATENT-VERWALTUNGS-GmbH 7 Aug 1972 [6 Aug 1971 27 Dec 1971] 36827/72 Heading C4S [Also in Division H1] An indirect band gap elementary semiconductor material, such as germanium or silicon, can be operated in a lasing mode by providing a structural non-uniformity in the light emitting region, the non-uniformity causing a displacement of the conduction band so that a direct band gap is obtained between an absolute secondary minimum of the conduction band and the absolute maximum of the valency band. The material is then equivalent to a direct band gap compound semi-conductor material such as gallium arsenide. The conduction band displacement is obtained by providing a periodic variation of the structure in the light emitting region in the crystallographic direction of an absolute secondary minimum of the conduction band, the periodic length of structure variation being of the order of the mean free path length of the conduction electrons in the semiconductor. This variation may be caused by dislocations or point effects in the crystalline structure or may be obtained by providing alternate bands 2, 3 of different doping concentration or by alloying, Fig. 2, in the light emitting region. The semi-conductor body may contain a P-N junction, Fig. 4 (not shown), and may further be of heterostructure formation, Fig. 6, in which a P-N junction is located in a laser active region 2 flanked by differently doped regions 1 and 3, the gap between the valency and conduction bands being least in the active region. An example uses an Si 1-x Ge z alloy for the active region 2 and an Si 1-y Ge y alloy for the outer regions 1, 3, where y < x. In addition to the main electrodes shown an auxiliary electrode may be provided, the main electrode current being maintained at below the lasing threshold and a laser output pulse being obtained each time the auxiliary electrode is pulsed. The laser may be mounted on a diamond heat sink. Light or electron beam pumping may be used in structures not formed with a P-N junction.